Annular dies, such as, for example, co-extruded blown film dies, are used to form multi-layer products, e.g., blown films, from thermoplastic melts (hereinafter “melt”). Typically, modular co-extruded blown film dies include a module formed of an assembly of cells. Each cell usually includes several annular disks and produces one layer of a multi-layer product. Because each cell normally produces only one layer, conventional modular annular dies producing multi-layer products tend to become more bulky as more layers are added.
Co-extruded blown film dies have progressed to more and more layers over the past twenty years in order to combine diverse materials valued for performance enhancement or film properties in order to make unique specialty films. Most are now in the range of 7 to 11 layers. All vary in thickness capabilities but all may be termed as being able to make films containing micro-scale layers (hereinafter “micro-layer”).
Annular co-extruded films, tubing and parisons can vary in total thickness to the extent to which the melt is drawn from the die. The faster a melt is drawn the thinner it will be. Corresponding micro-layers within the total film thickness will be likewise proportionally affected in thickness by the draw. So the absolute thickness of any micro-layer is a moving target and may be best expressed in terms of relative thickness. Micro-layers within the standard co-extruded films usually may vary in relative thickness over a range from 1% to 100% of the total thickness. This limitation is related to total output rate of the film line and the maximum residence time of the melts within the die system before the polymer melt starts to degrade.
For example, layers within a typical 10-mil thick multi-layer product produced by conventional or modular annular dies are considered micro-layers, and typically range in thickness from about 0.1 mil to about 10 mils, and conventional and modular annular dies typically produce multi-layer products having anywhere from about 7 to 11 layers. Because cells that produce micro-layers in a modular annular die are relatively thick, increasing the number of micro-layers in a multi-layer product typically undesirably increases the overall thickness of the module containing these cells. Other conventional annular dies also have similar dimensional limitations.
There is an ongoing need for an improved modular annular die for producing multi-layer products with more, thinner layers. There is an ongoing need for multi-layer products having a higher number of layers that produce synergistic material responses such as mimicking the properties of blends without the incompatibility issues generally associated with blends. There is also a need to have films with very thin nano-layer bundles dispersed within a matrix of micro-layers so that the synergistic behavior of multiple materials in nano-layer form is not shackled by loss of high strength seal performance. Finally, there is an ongoing need for multi-layer products having many layers squeezed into the thickness or height dimensions that characterize most annular co-extrusion dies.